The present invention relates to a formed surface mount resistor and method for making same.
Surface mount resistors have been available for the electronics market for many years. Their construction has comprised a flat rectangular or cylindrically shaped ceramic substrate with a conductive metal plated to the ends of the ceramic to form the electrical termination points. A resistive metal is deposited on the ceramic substrate between the terminations, making electrical contact with each of the terminations to form an electrically continuous path for current flow from one termination to the other.
An improvement in surface mount resistors is shown in U.S. Pat. No. 5,604,477. In this patent a surface mount resistor is formed by joining three strips of material together in edge to edge relation. The upper and lower strips are formed from copper and the center strip is formed from an electrically resistive material. The resistive material is coated with epoxy and the upper and lower strips are coated with tin or solder. The strips may be moved in a continuous path for cutting, calibrating, and separating to form a plurality of electrical resistors.
A primary object of the present invention is the provision of an improved formed surface mount resistor and method for making same.
A further object of the present invention is the provision of a method for making a formed surface mount resistor which utilizes a single ribbon of material for the resistor body and the carrier strip.
A further object of the present invention is the provision of an improved formed surface mount resistor and method for making same which reduces the number of steps and improves the speed of production from that shown in U.S. Pat. No. 5,604,477.
A further object of the present invention is the provision of an improved formed surface mount resistor and method for making same wherein the resulting resistor is efficient in operation and improved in quality.
A further object of the present invention is the provision of a formed surface mount resistor and method for making same which is economical to manufacture, durable in use and efficient in operation.
The foregoing objects may be achieved by a surface mount resistor comprising an elongated resistive body formed from a single piece of electrically resistive material. The resistive body includes first and second terminal ends and a raised center portion positioned above first and second terminal ends. The raised center portion includes first and second opposite edges and has a plurality of slots extending into the lateral edges so as to create a serpentine current path through the raised center portion from first terminal end to the second terminal end. A dielectric material surrounds and encapsulates the raised center portion. An electrically conductive material coats the first and second terminal ends.
The method for making the surface mount resistor of the present invention comprises taking an elongated ribbon of electrically resistive material having upper and lower ribbon edges. The ribbon is partially separated into a plurality of individual body members, each having opposite side edges and first and second terminal ends with a central portion therebetween. The ribbon includes a carrier portion interconnecting the plurality of body members. A plurality of slots are formed in the opposite side edges of the body members so as to create a serpentine current path from the first terminal end through the central portion to the second terminal end in each of the body members. The cross sectional shapes of the body members are then formed so that the central portion is raised above the first and second terminal ends. The raised central portion is then encapsulated within a dielectric material and the terminal ends of the body members are coated with an electrically conductive material.
In one embodiment of the method the step of forming the cross sectional shape of the body members is performed by forming the ribbon before the separating step is accomplished.
In another embodiment of the method of the present invention the step of forming the cross sectional shape of the body members is performed on the body members after the separating step has been performed.
Various types of forming methods may be used, including roll forming to create the forming of the raised portion or stamping may also be used. Preferably the roll forming method is used when the forming is accomplished before separating the strip into the various body members. Stamping is the preferred method if the forming is accomplished after the body members have been separated.